The present invention relates to an improved process for preparing bridged biscyclopentadienyl compounds.
Compounds of this type are starting components for, for example, chiral, stereorigid metallocene compounds which, in combination with cocatalysts, are used, inter alia, as stereospecific catalyst systems of high activity in the polymerization of olefins (EP-A-O 51 392).
There have therefore been many proposals in the past for preparing these bridged biscyclopentadienyl compounds, with the general reaction scheme ##STR1## wherein CpH is cyclopentadiene, R is a short-chain alkyl radical, Q is an alkyl or aryl radical, and X is Cl, Br, I or --O---tosyl being largely used. These processes have the disadvantage that they are carried out at temperatures .ltoreq.70.degree. C. using problematical solvents such as ethers, methylene chloride, chloroform or hexamethylenephosphoramide (HMPA). In addition, the yield of biscyclopentadienyl compounds was generally small and was further reduced by purification processes required (Journal of Organometallic Chemistry, 1988, 342, 21-29, DE-A 38 44 282).
It is therefore an object of the present invention to provide a process which makes possible the preparation of bridged biscyclopentadienyl compounds in substantially higher yields and high purity without technically complicated process steps.
This object was surprisingly achieved by reaction of biscyclopentadienylmagnesium compounds (CpR.sub.a).sub.2 Mg with suitable difunctional compounds XQX.sup.1.